(616d) Tunable Structural Color of Bottlebrush Block Copolymers through Direct-Write 3D Printing from Solution

Additive manufacturing of functional materials exhibiting tunable structural color remains highly challenging, due to the need for on-the-fly control of printed structures at the nanoscale. We overcome this challenge by integrating nonequilibrium self-assembly of bottle brush block copolymers with a highly versatile direct-write 3D printing approach. We demonstrate that by varying printing conditions during deposition, peak reflected wavelength for bottlebrush photonic crystals prepared from a single ink can be controlled across a range of 403 to 626 nm (blue to red), corresponding to a predicted change in d-spacing of >70 nm (Bragg-Snell equation). We further demonstrate spatial and functional patterning of photonic crystals to achieve colorful prints of chameleon patterns through on-the-fly tuning of assembly kinetics during printing. Via scanning electron microscopy and synchrotron small-angle X-ray scattering analysis of printed films, we then confirm the microstructural underpinning of this phenomena as tuning of lamellar domain d-spacing (total thickness of A+B blocks) which we attribute to modulation of polymer conformation during printing. Finally, we establish the role of kinetic trapping of metastable microstructures as the mechanism for domain size control based on in situ optical microscopy and solvent-vapor annealing experiments. Thus, we demonstrate a new method for tunable block copolymer photonics without synthetic variation. Furthermore, we present a hardware and software integrated 3D printing scheme that can serve as a test bed for functional property modulation for a variety of material systems.